What determines the circuit rating if using a conductor with an ampacity higher than 50 amperes?

The circuit rating is primarily determined by the ampere rating of the overcurrent device. This is because the overcurrent device, such as a fuse or circuit breaker, is designed to protect the conductor and connected equipment by limiting the current flowing through the circuit. If a conductor has an ampacity higher than 50 amperes, it means it can handle that amount of current safely without overheating. However, the actual rating for the circuit will be based on the rating of the overcurrent device, which ensures that the circuit is protected from excessive current that could potentially cause damage or create a fire hazard.

In a practical sense, even if the conductor can handle higher amperages, the overcurrent device must still be rated to allow safe operation of the entire circuit. This means that if the overcurrent device is rated at, say, 40 amperes, then the circuit will be rated at that level, regardless of the conductor’s capability to handle more. Thus, the overcurrent device plays a critical role in setting the safe operating conditions for the circuit.